1. Field of the Invention
This invention relates to a liquid crystal display.
2. Prior Art
Most liquid crystal devices are comprised of two spaced parallel substrates with liquid crystal between the substrates. Electrical conductors for the application of a selected voltage are formed on internal facing sides of the substrates. When a voltage is applied to the liquid crystal via the electrical conductors, the liquid crystal changes from a first state to a second state. Typically, in the first state, the liquid crystal is transparent, while in the second state it forms a light altering (e.g. scattering) surface at the point of voltage application.
By placing formed electrodes in certain desired locations specific images coinciding with the formed electrode can be selectively made to appear in the liquid crystal. For example, one form of the liquid crystal display unit employs front and rear transparent substrates, and is viewed from the front substrate. The front and rear substrates and front electrodes are transparent, while the rear electrode may be reflective or transparent. In addition, the rear substrate may employ an additional layer or coating to achieve certain desired optical effects. When the device is used, light is directed into the front side of the display and the electrodes are energized. Various parts of the liquid crystal become light scattering and the effect is to view scattering portions on a mirror-like background. There are, of course, other forms of liquid crystal display which do not employ the same physical effect but which may employ the invention described herein.
The operation and construction of liquid crystal display devices, such as described above, is well known in the prior art. Two examples of such prior art are U.S. Pat. No. 3,322,485 and U.S. Pat. No. 3,612,654.
There have been numerous problems in prior art liquid crystal display devices regarding the cosmetic appearance of the display devices. Haze formation within the liquid crystal is one such problem. Nematic liquid crystal has a particular molecular alignment when it comes in contact with any type surface. The molecular alignments tend to be different for each type of surface the liquid crystal is contacting. In the prior art the liquid crystal often contacted four or more different types of surfaces and this forced the liquid crystal to take as many different molecular alignments as surfaces it engaged. (The different molecular alignments cause the usual effect of a haze in the liquid crystal package.) The present invention tends to solve these problems by reducing to a minimum the number of different surfaces which the liquid crystal must contact.
Another problem in the prior art arises from the fragmented or pad like configuration of the back reflector. This configuration has resulted in the energized segment having one contrast to certain portions of the segment and another contrast as to other portions of the segments. This results in poor overall contrast. This is true regardless of the fact that a layer of material is employed on the side of the substrate opposed to that where the pads are formed. This problem is solved by the present invention by creating the appearance of a solid back reflector. A further benefit is that the unpowered segments are made less visible because there is no adjacent "bare" glass to provide optical contrast.
A primary characteristic of the liquid crystal display devices is that both substrates are required to be perfectly aligned both in the horizontal and vertical plane. The present invention reduces the necessity of perfect substrate alignment. The present invention embodies a structure which will allow mechanical alignment assembly techniques and result in substantial savings to manufacturers.
Another problem in the prior art occurs when direct current is applied to the liquid crystal display. The direct current tends to contaminate the liquid crystal, thereby lowering the useful life of the display. This problem in the present invention is solved by applying a dielectric coating to the conductive surface on each substrate which screens off any residual direct current which may be applied to the display. This dielectric coating or layer benefits the cosmetic appearance because it reduces the number of different surfaces the liquid crystal must contact. Thus, the possibility of haze formation is reduced even further.